Sandflies live on every continent except Australia and Antarctica, with the heaviest populations concentrated in tropical and subtropical regions of South America, Africa, the Middle East, South Asia, and the Mediterranean. They breed in surprisingly small, hidden spots close to the ground, which is why most people never see their nesting sites even in areas where bites are common.
It’s worth noting that the term “sandfly” can refer to two different insects depending on where you live. In tropical medicine, sandflies are tiny flies in the subfamily Phlebotominae that transmit diseases like leishmaniasis. In coastal areas of the US, Australia, and other English-speaking countries, people often call biting midges “sandflies.” These are a completely different insect family. This article covers true phlebotomine sandflies, the ones that matter for disease transmission, though it touches on the coastal biting midges as well.
Global Distribution
Phlebotomine sandflies have been documented in 88 countries, 72 of which are developing nations. In the Old World (Europe, Africa, and Asia), they range from the Mediterranean Basin across the Middle East and into northwest India, with scattered populations in Central China, West Africa, and the Horn of Africa. In the New World (the Americas), they’re found from the southern United States through Central America and deep into South America, with Brazil, Colombia, and Peru reporting especially large populations.
The countries with the most significant sandfly-borne disease burden tell you where these insects are most active. Over 90% of potentially fatal visceral leishmaniasis cases occur in just six countries: Brazil, Ethiopia, Sudan, South Sudan, India, and Bangladesh. For the skin form of the disease, ten countries account for 75% of global cases: Afghanistan, Colombia, Brazil, Algeria, Peru, Costa Rica, Iran, Syria, Ethiopia, and Sudan.
In southern Europe, sandflies are well established in countries like Tunisia, Morocco, Spain, Italy, and Greece. They thrive in the warm, dry summers typical of Mediterranean climates.
Sandflies in the United States
Several sandfly species live in the US, though they get far less attention than mosquitoes. Southern Texas has populations of Lutzomyia species suspected of transmitting cutaneous leishmaniasis. Other species are found throughout the Southeast. One species that feeds on reptiles has been documented as far north as Connecticut, and researchers confirmed its presence in upstate New York, where it was widespread and locally abundant in mature oak-hardwood forests. Another species that feeds on mammals has established populations in southern New Jersey.
These US populations are not currently major disease vectors for humans, but their range demonstrates that sandflies are not limited to far-flung tropical locations.
Where They Breed
Sandfly larvae need moist, organic-rich soil or debris to develop. Unlike mosquitoes, which lay eggs in standing water, sandflies deposit eggs in dark, sheltered spots on or just below the ground surface. The most productive breeding sites, based on field research in Colombia, include the buttress roots of large trees, the base of tree trunks, and tree holes. Leaf litter on forest floors is another common nursery. Caves, animal burrows, pig pens, chicken coops, and the bases of palm fronds have all yielded sandfly larvae as well.
What these sites share is darkness, consistent moisture, and decaying organic material that the tiny worm-like larvae feed on. Because the larvae are so small (just a few millimeters) and buried in debris, locating breeding sites in the wild is notoriously difficult. Researchers in Brazil found sandfly breeding sites evenly distributed within at least 60 meters of houses and animal shelters, meaning there wasn’t a clear “safe distance” from homes. If the surrounding environment has suitable soil and organic matter, sandflies breed throughout it.
Altitude and Terrain
Sandflies are not restricted to lowlands. In Peru, one species has been found at elevations up to 3,300 meters (about 10,800 feet) above sea level. In the lower Himalayas, species have been recorded above 3,000 meters. At the other extreme, sandflies live in areas below sea level near the Dead Sea. This enormous vertical range means that altitude alone doesn’t rule out sandfly presence. If temperatures and humidity fall within their survival window, sandflies can establish populations.
Temperature and Humidity They Need
Sandflies are warmth-loving insects. Their ideal temperature range sits between about 30°C and 33°C (86°F to 91°F), and humidity levels around 72% to 82% create peak activity conditions. Below 15°C (59°F) or above 32°C (90°F), their ability to reproduce and their lifespan drop significantly.
Temperature also controls how fast they develop. At 32°C, a sandfly can go from egg to adult in roughly 28 days. At 18°C, that same development stretches to about 246 days. This is why sandfly populations explode during warm, humid months and virtually disappear in cooler seasons. Rainfall plays a role too: moderate rainfall up to about 120mm per month supports higher sandfly numbers, likely because it keeps the soil moist enough for larvae without flooding breeding sites. The effect of rising temperatures and rainfall on sandfly density often shows up with about a two-month delay, reflecting the time it takes eggs and larvae to mature into biting adults.
Seasonal Activity Patterns
In tropical regions near the equator, sandflies can be active year-round, though their numbers still fluctuate with wet and dry seasons. In subtropical and temperate zones, they follow a more defined seasonal pattern, emerging in late spring or early summer and peaking during the warmest, most humid months. In the Mediterranean, for instance, sandfly season typically runs from May through October.
Drier zones with warm temperatures can actually be more favorable for sandfly survival than constantly wet tropical forests, because the combination of warmth and moderate humidity hits their biological sweet spot. This explains why some of the highest disease transmission rates occur in semi-arid regions like parts of the Middle East and North Africa rather than in dense equatorial rainforest.
Indoor vs. Outdoor Habitats
Most sandfly species feed and rest outdoors. They’re most active at dawn and dusk, sheltering during the day in shaded crevices, animal burrows, tree holes, and rock walls. However, some species are peridomestic or domestic, meaning they readily enter homes and animal shelters to feed and rest. These indoor-feeding species are the ones most responsible for transmitting disease to humans, since they bring the parasite directly into living spaces.
Sandflies are weak fliers. They don’t travel far from their breeding sites and fly in short, hopping bursts close to the ground. Wind speeds above a gentle breeze can ground them entirely. This limited flight range means that the sandflies biting you at night are almost certainly breeding within a short distance of your home, not migrating in from a distant habitat.
Coastal “Sandflies” Are a Different Insect
If you’re being bitten on a beach in Florida, Australia, or the Caribbean, the culprit is most likely a biting midge, not a phlebotomine sandfly. Biting midges belong to a different insect family (Ceratopogonidae) and live along the shores of oceans, lakes, ponds, and rivers. Their larvae develop in moist sand, wet soil, and rotting vegetation at water’s edge. They bite during the day or night, and while the bites are painful and irritating, these coastal insects don’t transmit leishmaniasis. In the US, their primary concern is transmitting bluetongue virus to livestock rather than diseases to humans.